Passive motion isolation system

ABSTRACT

A passive motion isolation system for motion-sensitive equipment is disclosed. The passive motion isolation system has a three-axis free motion platform mounted on a base subject to ambient motions. A vibration isolation subsystem is coupled between the motion-sensitive equipment and the three-axis free motion platform.

CROSS-REFERENCE

This application is a continuation of U.S. Utility application Ser. No.16/803,053 filed Feb. 27, 2020, which claims the benefit of U.S.Provisional Application No. 62/815,743, filed Mar. 8, 2019, entitledPassive Motion Isolation System which applications are incorporatedherein in its entirety by reference.

BACKGROUND Field

This disclosure relates to motion isolation systems for motion-sensitiveelectronic equipment.

Description of the Related Art

Motion-sensitive electronic equipment may include, and/or be mounted on,elastic vibration isolators. A particular combination of a piece ofequipment and a vibration isolator will have a natural resonantfrequency. The vibration isolator may be effective to minimize orprevent coupling of vibrations from the ambient to the equipment forvibration frequencies significantly higher than the resonant frequency.However, the frequency spectrum of ground motion due to earthquakes maybe concentrated at frequencies below 3 Hertz and may include significantmotion at frequencies of 0.5 Hz or lower. It is generally impractical tolower the resonant frequency of vibration-isolated equipment to lessthan 0.5 Hz. Thus conventional vibration isolation systems may beineffective at isolating the equipment from low-frequency motions suchas those caused by earthquakes.

SUMMARY

An aspect of the disclosure is directed to motion isolation systems formotion-sensitive equipment. Suitable motion isolation systems comprise:a base subject to ambient motions; a three-axis free motion platformmounted on the base; and a vibration isolation subsystem coupled betweenthe motion-sensitive equipment and the three-axis free motion platform.

Additionally, the three-axis free motion platforms are configurable tocomprise: an x-axis free motion stage and a y-axis free motion stage,the x-axis and the y-axis orthogonal to each other and essentiallyhorizontal, and a z-axis free motion stage, the z-axis being orthogonalto both the x-axis and the y-axis and essentially vertical. For example,the x-axis free motion stage can comprise an x-axis carriage free tomove along an x-axis rail, the y-axis free motion stage comprises ay-axis carriage free to move along a y-axis rail, and the z-axis freemotion stage comprises a z-axis carriage free to move along a z-axisrail. Additionally, in some configurations the y-axis rail is attachedto, and moves with, the x-axis carriage, the z-axis rail is attached to,and moves with, the y-axis carriage, and the vibration isolationsubsystem is coupled between the z-axis carriage and themotion-sensitive equipment. In some configurations it might be desirablefor the z-axis free motion stage to comprise a counterbalance mechanismto offset a total weight of the z-axis carriage, the vibration isolationsubsystem, and the motion-sensitive equipment. The counterbalancemechanism can additionally comprise at least one constant force spring.Each of the x-axis rail, the y-axis rail, and the z-axis rail can beconfigurable to have a finite length between respective ends, in whichcase the system can further comprise: a plurality of resilient firmstops, a firm stop from the plurality of firm stops located proximateeach end of each of the x-axis rail, the y-axis rail, and the z-axisrail to limit a range of motion of the respective carriage in bothdirections along the rail. Motion isolation systems can also have aplurality of resilient soft stops, a soft stop from the plurality ofsoft stops located proximate each end of each of the x-axis rail, they-axis rail, and the z-axis rail, wherein each soft stop is configuredsuch that a carriage nearing an end of the respective rail contacts thesoft stop located proximate the end of the rail before contacting thecorresponding firm stop. Each soft stop can also be configured to extendfurther along the respective rail and has a smaller cross-sectional areathan the corresponding firm stop. At least some configurations of thevibration isolation subsystem can further comprise: a support attachedto the z-axis carriage; four elongate resilient pillars, each pillarhaving a first end affixed to the support, a length extending from thesupport parallel to the z-axis, and a second end; and a mountingstructure to couple the motion-sensitive equipment to the second ends ofthe four pillars. The mounting structure can also be configured suchthat all or a portion of the motion-sensitive equipment is disposedbetween the four pillars.

In some configurations the mounting structure is configured such thatthe motion-sensitive equipment does not contact the four pillars and thesupport. Each of the four pillars can further comprise first and secondsegments, the vibration isolation subsystem can also further comprise afirst frame, the first segments of each of the four pillars can beconfigured to couple the mounting structure to the first frame, and thesecond segments of each of the four pillars couple the first frame tothe support. Each of the four pillars can further comprise first,second, and third segments, the vibration isolation subsystem canfurther comprise first and second frames, and the first segments of thefour pillars can couple the mounting structure to the first frame, thesecond segments of the four pillars couple the first frame to the secondframe, and the third segments of the four pillars couple the secondframe to the support. In other configurations at least one motionlimiter can be provided to limit a range of motion of the mountingstructure with respect to the support. One or more motion limiter canfurther comprise one or more of a resilient grommet attached to thesupport, and a post extending from the mounting structure through acenter hole in the resilient grommet.

Another aspect of the disclosure is directed to methods of using thedisclosed motion isolation systems for motion-sensitive equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 is a schematic depiction of a passive motion isolation system;

FIG. 2 is a perspective view of a motion isolation system;

FIG. 3 is a front view of the motion isolation system of FIG. 2 ;

FIG. 4 is an end view of the motion isolation system of FIG. 2 ;

FIG. 5 is a back view of the motion isolation system of FIG. 2 ;

FIG. 6 is a perspective view of a multi-axis motion platform used in themotion isolation system of FIG. 2 ;

FIG. 7 is another perspective view of the multi-axis motion platform ofFIG. 6 ; and

FIG. 8 is a perspective view of a portion of a vibration isolationsubsystem showing details of a motion limiter.

DETAILED DESCRIPTION

FIG. 1 is a schematic depiction of a motion isolation system 10 thatemploys a tiered or stacked structure to isolate motion-sensitiveequipment 15 from vibration and movement introduced through a base 40.The equipment 15 is coupled to the base 40 through a two-tieredstructure including a vibration isolator 20 and a low-frequency motionisolator 30. The base 40 is subject to ambient movement including, butnot limited to, vibrations caused by machinery or traffic; and buildingmotions due to earth quakes. The combination of the equipment 15 and thevibration isolator 20 may have a natural resonant frequency. Thevibration isolator 20 may be effective to minimize or prevent couplingof vibrations from the base 40 to the equipment 15 for vibrationfrequencies significantly higher than the resonant frequency. Thelow-frequency motion isolator 30 isolates the motion-sensitive equipment15 from small-amplitude motions of the base 40 for frequenciescomparable to, or less than, the resonant frequency. The low-frequencymotion isolator 30 isolates larger amplitude low-frequency motions, suchas motions caused by earthquakes, so that they are coupled to themotion-sensitive equipment 15 with limited acceleration that may notsubstantially degrade the performance of the motion-sensitive equipment

FIG. 2 is a perspective view of a motion isolation system 100 which isan embodiment of the motion isolation system 10 of FIG. 1 . FIG. 3 ,FIG. 4 , and FIG. 5 are front, end, and back views, respectively of themotion isolation system 100. The relative position of various parts ofthe motion isolation system 100 will be described based upon theseviews. Throughout this description, terms indicating direction, relativeposition, or size (e.g. “up”, “down”, “left”, “right”, “over”, “under”,“height”, “width”, etc.) may be used when referring to the drawingfigure

As shown in FIG. 2 , the motion isolation system 100 includes avibration isolation subsystem 200 and a multi-axis motion platform 300.Equipment module 110 is supported by the vibration isolation subsystem200 which is an embodiment of the vibration isolator 20. The vibrationisolation subsystem 200 is mounted on the multi-axis motion platform300, which is an embodiment of the low-frequency motion isolator 30. InFIGS. 2-7 , x, y, and z axes are defined for ease of description of theelements of the motion isolation system. In FIGS. 3-8 , components ofthe vibration isolation subsystem 200 are identified by referencedesignators between 210 and 270. Components of the multi-axis motionplatform 300 are identified by reference designators between 310 and375.

The vibration isolation subsystem 200 is supported by a support 240which is attached to the multi-axis motion platform 300. In thisexample, the support 240 is a rigid metal plate. The support 240 may bea plate, a frame, or some other rigid structure. Four elongatedresilient pillars 250A, 250B, 250C, 250D, of which only 250A and 250Bare visible in FIG. 3 , extend upward from the support 240. The othertwo elongated resilient pillars 250C, 250D are located behind theequipment module 110 as shown in FIG. 5 . Each elongated resilientpillar 250A-D has a first end affixed to the support 240, a lengthextending parallel to the z-axis, and a second end remote from thesupport 240. The equipment module 110 is coupled to the second ends ofthe four elongated resilient pillars 250A-D by a mounting structure 210.In this example, the mounting structure 210 consists of two supportbrackets 215, only one of which is visible in FIG. 3 . A second supportbracket (which is a mirror image of the support bracket visible in FIG.3 ) is located behind the equipment module as shown in FIG. 5 . The twosupport brackets 215 are attached to the second ends of the fourelongated resilient pillars 250A-D (each support bracket attaches to twoof the elongated resilient pillars 250A-D) and extend downward from aplane defined by the second ends of the four elongated resilient pillars250A-D. The overall height (i.e., dimension parallel to the z-axis) ofthe four elongated resilient pillars 250A-D is greater than a height ofthe equipment module 110 such that the bottom of the equipment module110 is suspended above the support 240. Other mounting structures may beused to couple an equipment module to the four elongated resilientpillars 250A-D such that all or a portion of the equipment module isdisposed between the elongated resilient pillars 250A-D and above thesupport 240.

To prevent excess lateral or rotational motion of the equipment module110, each of the four elongated resilient pillars 250A-D may be dividedinto two or more segments, with joints between the segments connectedtogether by frames that connect the four elongated resilient pillars250A-D without contacting the mounting structure 210 or equipment module110. In this example, each elongated resilient pillar 250A-D is dividedinto upper pillar segment 252, middle pillar segment 254, and lowerpillar segments 256 as shown in FIGS. 3, 5 and 8 . The mountingstructure 210 is coupled to a first frame 220 by four upper pillarsegments 252, of which only two are visible in FIG. 3 . The first frame220 is coupled to a second frame 230 by four middle pillar segments 254,of which only two are visible in FIG. 3 . The second frame 230 iscoupled to the support 240 by four lower pillar segments 256, of whichonly two are visible in FIG. 3 . The upper pillar segment 252, middlepillar segment 254, and lower pillar segment 256 may be made from aresilient or viscoelastic material such as a polyurethane foam. Theupper pillar segment 252, middle pillar segment 254, and lower pillarsegment 256 may be attached to the associated mounting structure 210,first frame 220, second frame 230, and support 240 by adhesive. Twomotion limiters 260 (of which only one is visible in FIG. 2 ) limit therange of motion of the mounting structure 210 and equipment module 110with respect to the support 240. The motion limiters will be describedin additional detail in conjunction figure FIG. 8 .

The left and right ends of the first frame 220 are twice folded to forma vertical portion 222 and a horizontal portion 224 that passes underthe equipment module 110. The second frame 230 is similarly folded.Alternatively, the first frame 220 and the second frame 230 could beunfolded. In this case, the ends of the first and second frame willextend beyond the left and right ends of the equipment module 110 (notshown). The folded-frame configuration shown in FIG. 3 is more compact.

The number of segments in each pillar and the number of frames in thevibration isolation subsystem 200 may be tailored to the size and massof the equipment module. A vibration isolation subsystem may have moreor fewer than three segments in each pillar and more or fewer than twoframes. The number of segments in each pillar will be equal to thenumber of frames plus one.

FIG. 4 is an end view of the motion isolation system 100 showing theequipment module 110, the two support brackets 215, the two motionlimiters 260, two upper pillar segments 252 of elongated resilientpillars 250B and 250C. It also shows vertical portions 222 andhorizontal portion 224 of the first frame 220. The multi-axis motionplatform 300 includes an x-axis/y-axis (e.g., x-axis and y-axis) motionstage 310 and a z-axis motion stage 350. Although not visible in FIG. 4, the support 240 of the vibration isolation subsystem 200 is attachedto a movable portion of the z-axis motion stage 350.

A motion stage is a mechanical device including a carriage that ismovable in a linear direction along an axis defined by a guide. Afree-motion stage is a motion stage where the carriage is free to movewith respect to the guide, rather than driven by a motor or otherpositioning device. A motion isolation system that uses only free-motionstages may be considered passive. The guide may be a single rail havinga rectangular, triangular, trapezoidal, or x-shaped cross-section, achannel having a u-shaped cross-section, a pair of parallel ways(commonly having circular cross-sections), or some other elongatestructure that defines a direction of motion of the carriage. Thecarriage may be configured to move freely along the guide in the defineddirection and may be constrained to not move in directions orthogonal tothe defined direction. Typically, a carriage is in contact with two ormore surfaces of the guide to prevent motion in directions orthogonal tothe defined direction. Friction at the points of contact between acarriage and a guide may be minimized through the use of ball bearings,roller bearings, bushings, lubricants, and/or other devices. Since thelength of a guide must be finite, a motion stage typically includesstops to prevent a carriage from moving past the ends of the guide.

Motion stages may be stacked to allow motions along multiple axis. Forexample, a first motion stage may include a first rail and a firstcarriage that moves along the first rail in a first direction. A secondrail may be attached to the first carriage such that the second rail isnot parallel to the first rail. Typically, the second rail may beperpendicular to the first rail. The second carriage moves along thesecond rail in a second direction, and the second carriage, second rail,and first carriage are free to move, as a unit, along the first rail inthe first direction. Similarly, a third rail may be attached to thesecond carriage, with the third rail typically extending in a directionperpendicular to both the first and second rails.

In the motion isolation system 100, the x and y axes are defined as twoorthogonal axes, each of which is essentially horizontal. The z axis isdefined to be orthogonal to both the x and y axes and thus essentiallyvertical. The directions of each of the x and y axes are consideredessentially horizontal if a component of gravity along both of the x andy axes is insufficient to cause motion of the corresponding carriagealong the respective axis of the x-y motion stage 310.

FIG. 5 is a back view of the motion isolation system 100. The equipmentmodule 110, one of the support brackets 215, the first frame 220 andsecond frame 230, the support 240, upper pillar segment 250, middlepillar segment 254, lower pillar segment 256 of elongated resilientpillars 250C and 250D, and one of the two motion limiters 260 arevisible.

The z-axis motion stage 350 includes a z-axis carriage 360 that slidesalong a z-axis rail 355. The support 240 is attached to the z-axiscarriage 360 such that the z-axis carriage supports the vibrationisolation subsystem 200, and the equipment module 110. Since the z-axisis essentially vertical, gravity will attempt to pull the z-axiscarriage 360 to its lowest position. To allow the z-axis carriage tofloat along the z-axis rail without being pulled to its lowest positionby gravity, the total weight of the z-axis carriage 360, the vibrationisolation subsystem 200, and the equipment module 110 is offset orcounterbalanced in the upward direction with a force equal to the totalweight. In an exemplary motion isolation system 100, two constant forcesprings 365 are used to counterbalance the weight of the z-axis carriage360, the vibration isolation subsystem 200, and the equipment module110. Other techniques to counterbalance this weight may be used.

FIG. 6 and FIG. 7 are perspective views of the multi-axis motionplatform 300, including the x-y motion stage 310 and the z-axis motionstage 350. Note that the constant force springs 365 are not shown inFIG. 6 to allow visibility of other portions of the z-axis stage 350.The x-y motion stage 310 includes a base 305 that supports an x-axisrail 315. The base 305 is subject to ambient movement including, but notlimited to, vibrations caused by machinery or traffic, and buildingmotions due to earth quakes. An x-axis carriage 320 slides along thex-axis rail 315. The x-axis carriage 320 supports a y-axis rail 325. Ay-axis carriage 330 slides along the y-axis rail 325. The z-axis rail355 is supported by the y-axis carriage 330.

The ranges of motion of the carriages 320, 330 along the respectivex-axis and y-axis rails 315, 325 are limited by resilient stops. Forexample, motion of the y-axis carriage 330 to the left (as seen in FIG.6 ) along the y-axis rail 325 limited by a soft stop 340 and a firm stop335. Although not clearly visible or identified in FIG. 6 , similar softand firm stops are positioned at the other end of the y-axis rail 325and both ends of the x-axis rail 315. The range of motion of the z-axiscarriage 360 is limited by soft stops 370 and 375 and firm stops 380 and385.

The soft stops and firm stops may be made from a resilient orviscoelastic material. Each soft stop (such as the soft stop 340) can beconfigured to have a longer length and smaller cross-sectional area thaneach firm stop (such as the firm stop 335). As will be appreciated bythose skilled in the art, the length of a stop can be measured along therespective motion axis and the cross-sectional area of a stop ismeasured in a plane orthogonal to the motion axis. A carriage nearingthe end of its motion range first contacts a soft stop. The soft stopthen compresses and/or deforms to gradually decelerate, but notnecessarily stop, the motion of the carriage. The soft stops may beinclined and/or curved with respect to the respective motion axis toensure both compression and deformation occur. The motion of thecarriage is stopped when the carriage reaches a firm stop.

Within the limits of the soft stops and firm stops, the x-, y-, andz-axis carriages 320, 330, 360 are free to move along the respectiverails. The range of free motion and the material, shape, andcross-sectional area of the soft and firm stops may be configured basedon the weight to be mounted on the x-y motion platform and theenvironment in which the motion isolation system will be used. The rangeof free motion may be, for example, one inch or greater along each axis.In another configuration the range of free motion may be, for example,between 1 and 12 inches along each axis.

When the base 305 is subjected to low frequency ambient movementssmaller than the free travel range of the carriages 320, 330, 360,inertia may cause one or more of the carriages to slide along theirrespective axis rails 315, 325, 355 while the base 305 moves. In thiscase, the vibration isolation subsystem 200 and the equipment module 110may remain substantially stationary. When the base 305 is subjected tolarger low frequency movements, one or more of the axis rails 315, 325,355 may move sufficiently to cause a soft stop to contact the respectivecarriage 320, 330, 360. In this case, the soft stop will graduallycompress and/or deform, coupling the movement of the base to the stageas a gentle acceleration. The length, cross-sectional shape, andmaterial of the stops and the free travel range of the carriages withrespect to the rails may be configured such that the worse-caseanticipated motions of the base do not disrupt or damage the equipmentmodule. Higher frequency vibrations of the base may be coupled throughthe multi-axis motion platform 300 to be attenuated by the vibrationisolation subsystem 200 (see FIG. 3 ).

FIG. 8 is a perspective view of a portion of the vibration isolationsubsystem 200 showing one of the motion limiters 260. The motion limiter260 includes a post 262 which is anchored at one end to the mountingstructure 210 that supports the equipment module 110. The post 262extends through a center hole in a grommet 264. The grommet 264 extendsthrough a ring 266 that is attached to the support 240. Motion of themounting structure 210 with respect to the support 240 in a plane normalto the axis of the post 262 is limited by the post 262 contacting aninner surface of the grommet 264. A washer 270 may be attached to alower surface (as shown in FIG. 8 ) of the ring 266. Motion of themounting structure 210 with respect to the support 240 along the axis ofthe post 262 is limited by an enlarged head 268 of the post 262contacting the washer 270. The grommet 264 and the washer 270 may beformed from a resilient or viscoelastic material such as a polyurethanefoam. The grommet 264 and the washer 270 may be two separate pieces orcombined into a single physical piece. The grommet 264 and the washer270 may be attached to the ring 266 by adhesive bonding or some othermethod.

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. It is intended thatthe following claims define the scope of the invention and that methodsand structures within the scope of these claims and their equivalents becovered thereby.

What is claimed:
 1. A motion isolation system for motion-sensitiveequipment, comprising: a base subject to ambient motions; a three-axisfree motion platform mounted on the base; and a vibration isolationsubsystem coupled between the motion-sensitive equipment and thethree-axis free motion platform.